Posted | filed under Weekly Reports.

With most of spring migration complete, the Lesser Slave Lake Bird Observatory is shifting gears to prepare for our breeding-focused projects beginning next week. Few species are still on the move. Yet, among the usual late migrating Alder Flycatchers, Mourning Warblers, and Canada Warblers have been a couple infrequent migrants with little in common with each other.  

Our first of these uncommon captures were Wilson’s Warblers. This species gets its name from Alexander Wilson, a pioneering ornithologist who himself first described them as the “Green Black-capt Flycatcher”, which ends up being a poor name as they are neither flycatchers nor often described as green. Instead, Wilson’s Warblers are foliage gleaning insectivores who are bright yellow almost everywhere except their plain gray undertail, their slightly olive-yellow back and (on males) their black crown.

Above: This Wilson’s Warbler was a young male banded on June 2, 2023. You can just make out his moult limit, but young males like this tend to have the olive edging to their crown feathers where a bird hatched earlier than last year will have completely black feathers in the crown.

Although Wilson’s Warblers have a wide range covering much of Canada’s boreal and montane landmass, we are located on the south-eastern edge of their Albertan range. Moreover, they prefer open woodlands near wetlands and are not often found in the thick, old-growth deciduous forests around our nets. With three banded this week, we are around our average for their spring captures, but well below the record of 23 banded in spring 2000. We seem to be seeing less and less of this species and these three Wilson’s Warblers were the first we have banded during spring since 2017. These declines are not unlike those found by the North American Breeding Bird Survey which has found cumulative declines in Wilson Warbler populations of around 60% since the 1960’s largely attributed to habitat loss on the breeding grounds.

The second of our uncommon captures were three Gray Catbirds. In stark contrast to the bright Wilson’s Warbler, Gray Catbirds are almost entirely dark gray aside from their reddish undertail coverts, though both sexes have a black cap like a Wilson’s Warbler. They are so-named by their call notes which sound much like a meowing cat. Their song often takes the form of jumping between impressions of other bird’s songs for up to ten minutes.

Above: Gray Catbirds, like this one also banded on June 2, 2023, cannot be easily sexed just by their plumage.

Gray Catbirds are much more common anywhere south of the boreal to the central United States. Where we are on the southern edge of the Wilson’s Warbler’s range, we are on the northern edge of the Gray Catbird’s. Catbirds enjoy foraging on fruits in small thickets and seem especially fond of the shrubbery around our parking lot. Due to their easy-to-meet diet and habitat preferences, their populations are fairly stable across their range. However, where we have seen declines in Wilson’s Warblers, we are seeing increases in Catbirds. To-date we have only banded thirteen Catbirds since 1993, and seven of these (over half) were banded since 2018.

We look forward to comparing other ways this spring to our past season in our next article after we wrap up spring migration monitoring on June 10.

By Robyn Perkins, LSLBO Bander-in-Charge